This invention is broadly concerned with the time delayed application of engine manifold vacuum to various engine control systems. Specific embodiments of the invention include exhaust gas recirculation control systems and carburetor idle enrichment systems both of which may be combined to provide an overall engine vacuum control system for improved emission control and improved vehicle driveability.
Motor vehicles driven by internal combustion engines make use of exhaust gas recirculation in order to recirculate portions of the internal combustion engine exhaust back to engine combustion chambers for suppressing to some extent the formation of NO.sub.x in the engine exhaust. This introduction of inert substances, i.e., combusted exhaust gas, into the combustion chamber is believed to lower peak combustion temperatures thereby reducing NO.sub.x formation. An EGR valve is used to control recirculation of the exhaust gas. The valve is typically a vacuum operated valve.
Carburetor idle enrichment systems are desirable additions to carburetor fuel control systems for internal combustion engines since they improve engine operation. Such systems provide a richer fuel/air mixture for a period of time after a cold start. In typical systems enrichment occurs when a vacuum is applied to a diaphragm controlled valve in the carburetor. The valve decreases the amount of air entering the idle air bleed resulting in a richer mixture.